It was previously known that biaxially oriented acrylonitrile polymer film could be produced from a melt composition of acrylonitrile polymer, see M. M. Zwick, U.S. Pat. No. 4,301,112, issued Nov. 17, 1981. It was also known that polyolefins in the form of diluted melts could be extruded to form fibrillated strands, see H. Blades et al., U.S. Pat. No. 3,081,519, issued Mar. 19, 1963. R. A. Blickenstaff, U.S. Pat. No. 4,094,948, issued June 13, 1978, teaches spinning water-assisted acrylonitrile polymer melts. A. Goodman et al., U.S. Pat. No. 3,896,204, issued July 22, 1975, teaches an improvement in the Blickenstaff process wherein the acrylonitrile polymer melt is obtained with the assistance of water and a small amount of a compatible solvent for the polymer. H. Porosoff, U.S. Pat. No. 4,163,770, issued Aug. 7, 1979, teaches spinning fusion melts of acrylonitrile polymer and water into a steam-pressurized solidification zone wherein the resulting filament is stretched.
H. G. Schirmer, U.S. Pat. No. 3,403,203, issued Sept. 24, 1968, teaches a non-woven fabric-like member which comprises mixing a blowing agent with a normally solid thermoplastic polymer at elevated temperature, heating the mixture in a confined zone at a temperature above the softening point of the polymer and at an elevated pressure sufficient to prevent expansion of the blowing agent gas, extruding the mixture through an annular die into an area of reduced pressure thereby forming a tubular shaped cellular structure, immediately inflating the tube by interiorly applying fluid pressure sufficient to rupture a substantial portion of the cells and form a non-woven fabric-like member, restricting the flow of fluid from within the resultant porous fabric-like member by enclosing at least the portion of the inflated tube with ruptured cells with a fluid impermeable member to reduce the loss of fluid pressure and deflating and cooling said tube below the softening point thereof.
H. G. Shirmer, U.S. Pat. No. 3,539,666, issued Nov. 10, 1970, teaches a variation of U.S. Pat. No. 3,403,203 in which the inflated tube is drawn over a shaped surface.
R. Woodell, U.S. Pat. No. 3,655,498, issued Aug. 11, 1972, teaches a process for preparing plexifilamentary structures which involves a flash extrusion process wherein a non-crystalline synthetic organic polymer in a liquid solvent under superatmospheric pressure and at a temperature in excess of the boiling point of the liquid solvent at atmospheric pressure is extruded through an orifice into a region of lower pressure. The flash evaporation of the solvent precipitates the polymer in the form of numerous fibrils which are interconnected at their ends in a three-dimensional array to form a flexifilamentary product.
H. W. Keuchel, U.S. Pat. No. 4,085,175, issued Apr. 18, 1978, teaches a process for producing a non-woven fibrous network comprising extruding a mixture of molten thermoplastic polymer and a foaming agent radially under compression through a circular die having a die gap transverse to the axis of the die head, applying radial stress to attenuate the polymer to form a molten fibrous cellular extrudate, maintaining radial stress over the molten extrudate to further attenuate said extrudate, quenching the extrudate to a temperature below its melting or flow temperature and further radially stretching said extrudate to provide a balanced non-woven fibrous network. The polymer forms a pure melt and, preferably, the foaming agent is blown into the melt during processing. Stretching of the film is in the radial direction and in the machine direction upon wind-up of the flattened film drawn at an angle of 75.degree.-125.degree. to the radial direction.
In Japanese Patent No. 83,205,503, a mixture of 80 weight percent cellulose acetate and 20 weight percent polydifluoroethylene in dimethyl formamide is spread on a glass plate and dried. The dried film is removed from the plate and stretched to produce a porous membrane used to separate kerosine and water.
In spite of the above-enumerated efforts in producing porous films, none of which have proven to be of substantial commercial interest, there continues to exist the need for improved processes therefor and for improved products resulting therefrom. The development of such process and product would fulfill a long-felt need and constitute a significant advance in the art.